This application is based on Japanese Patent Application No. 11-290264 (1999) filed Oct. 12, 1999, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an apparatus for evaluating the performance of a magnetic disk (a so-called spin stand) used in a hard disk drive.
2. Description of the Related Art
A hard disk drive (hereinafter referred to as HDD) is widely used as an information storage apparatus.
FIG. 1 shows a schematic diagram showing the structure of HDD which is now widely used. A magnetic disk 1 of HDD is rotated at a high speed of several thousand rpm by a spindle motor 2. A slider 4 positioned at the tip of a rotary positioner 3 is slightly floated by air stream flowing on the magnetic disk 1. Further, a magnetic head 5 is positioned at an end of the slider 4. The magnetic disk 1 is magnetically written with a servo signal, which signal is demodulated by a servo demodulation circuit 7 through a preamplifier 6, thereby obtaining a track information (representing on which track the head is positioned) and a PES signal (Position Error Signal representing how much the head is deviated from the track center).
The HDD, by reading the servo signal by the magnetic head 5, knows the present head position, drives the rotary positioner 3 by a voice coil motor (VCM) 8, and performs positioning on a track (target track) written with necessary information. That is, a difference between the target track position and the head position is detected as the PES signal which is inputted into a compensator 9. Next, the compensator 9 produces a drive instruction of the rotary positioner 3 based on the PES signal, and the rotary positioner 3 is driven by the voice coil motor (VCM) 8 through a power amplifier 10.
Here, on the magnetic disk 1 used in the HDD, the above servo signal and data are recorded and reproduced using the magnetic head 5. At this moment, since, if there is a defect in the magnetic disk, recording or reproduction cannot be performed satisfactorily, it is necessary to test that the necessary minimum performance is satisfied by the magnetic disk 1 before incorporating it in the HDD (that is, clamping the magnetic disk 1 to the spindle motor 2). In general, this test is performed using a magnetic head for testing, for successively testing a gliding characteristic, certify characteristic, and a contact start-stop (CSS) characteristic of the magnetic disk 1. In the gliding characteristic test, the number of protrusions on the magnetic disk 1 is checked, in the certify characteristic check, an electrical characteristic of the magnetic disk 1 and presence of a defect is checked, and in the CSS characteristic check, a durability characteristic of the magnetic disk 1 is checked. The magnetic disk performance tester used in this case is generally called as a spin stand.
FIG. 2 shows a schematic diagram showing the structure of a spin stand which is generally used. This spin stand comprises a base 11 as a support table of the apparatus, a spindle motor 12 provided on the base 11 for rotating the magnetic disk 1 for testing at an optional rotational speed, a magnetic head 13 for testing for reproducing or recording a signal on the magnetic disk 1 for testing the magnetic disk 1, a carriage 14 for mounting the magnetic head 13 for testing, a xcex8 stage 15 for adjusting the carriage at an optional angle, and a stage 16 (this stage 16 is movable in the horizontal direction in FIG. 2 along a guide 17) movable at least in one direction for flexibly changing the positional relation of the spindle motor 12 to the magnetic head 13 for testing.
The HDD of the head positioning type by the rotary positioner using the voice coil motor (VCM) is now widely used. Although it has an advantage of compact structure, it has a problem in that the head skew angle tends to vary at every track. The head skew angle relates to a floating amount of the magnetic head, which appears as a change in readback output from the head. Therefore, for a performance test of the magnetic disk 1, when the above gliding characteristic check, certify characteristic check, and CSS characteristic check are performed, it is necessary to perform the checking with the same skew angle as the HDD. Then, when performing checking, it is necessary that the positional relation of the spindle motor 12 and the magnetic head 13 for testing of the spin stand is adjusted to be the same as the checking HDD. Therefore a spin stand is normally used which is provided with a positioning mechanism by linear type stage 16 or a rotary type xcex8 stage 15 or the like.
Next, the magnetic disk 1 which is checked using the above spin stand and passed the checking is clamped to the spindle motor 2 and assembled as HDD. Then, in the state with the magnetic disk 1 incorporated in the HDD (that is, in the state with the magnetic disk 1 clamped to the spindle motor 2), a servo signal is written on the magnetic disk 1 by a device called a servo track writer (STW).
FIG. 3 shows an example of the structure when servo track write is performed by the servo track writer (STW). In the past, the servo track writer (STW), while being positioned by pressing a pin 19, which is exactly positioned by an external actuator 18, against the rotary positioner 3 in the HDD through a link 20, determines the head position by a fine feed mechanism according to a scale in the actuator 18. Because the servo signal is written in each track on the magnetic disk 1, the servo track writer (STW) writes the servo signal while being exactly positioned through the link 20 on all tracks on the magnetic disk 1.
However, recently with improvement of recording density, the number of tracks is increased, the track width is decreased, and the servo track writer (STW) is required to perform higher precision positioning on increased tracks. Because a high rigidity, high-cost mechanical positioning mechanism is required to achieve high precision positioning and an extended time is required for writing, a plurality of servo track writers (STW) are necessary for parallel processing therefore, more space is required for a clean room to dispose the servo track writers (STW), resulting in a cost increase.
Then, recently, it is considered to omit the above servo track writer (STW) and write the servo signal on the magnetic disk 1 from the beginning. For example, a method to copy the servo signal using a magnetic printing technique, a method in which a magnetic disk substrate having recesses and protrusions corresponding to the servo signal is formed by a stamper and a magnetic layer is formed on the substrate, and the like are proposed. With these methods, writing of the servo signal can be remarkably accelerated compared with the use of the servo track writer (STW).
However, when the servo signal is previously written on the magnetic disk alone by such methods, it is impossible to test the performance of the magnetic disk by testing of a single magnetic disk such as the above-described gliding characteristic testing, certify characteristic testing, and CSS characteristic testing. That is, in addition to the prior art inspection, it is necessary to confirm that head positioning is possible by a previously recorded servo signal.
The above-described prior art spin stand has the following problems.
(1) First problem
Since testing by the prior art spin stand is performed with the same skew angle as the HDD, it is necessary to adjust the positional relation of the spindle motor of the spin stand and the positioner to the same as the HDD, therefore a spin stand provided with a positioning mechanism such as of a linear or rotary stage or the like is normally used. As described above, in the past, the magnetic head is positioned by a stage, the positioning is structurally much different from the method in which head positioning of the rotary positioner is performed by the voice coil motor (VCM) as in the actual HDD.
Further, the gliding characteristics testing, certify characteristic testing, and CSS characteristic testing such as those in the prior art have been sufficient to evaluate with positioning as stage. However, from the point of view of servo performance test which is recently required, the prior art tester (spin stand) cannot perform sufficient testing. That is, to perform correct servo performance test, it is necessary to check whether or not the magnetic head is positionable in the same condition as of the actual HDD.
More specifically, position error factors in tracking control to follow the magnetic head to the track (positioning on the track) include track runout, measurement noise, and accelerational (or force) external disturbance. The track runout is a displacement viewed from the track position on the magnetic disk, which is divided into RRO synchronization with the disk rotation and NRRO not synchronization. Here, RRO is considered to be caused by eccentricity of mounting the magnetic disk to the spindle motor or an eccentricity of spindle motor itself. On the other hand, NRRO is considered as due to eccentricity of the spindle motor itself caused by the bearing or the like.
Further, the measurement noise is mainly an electrical noise related to the head medium characteristic or reproduction circuit. The accelerational external disturbance includes windage loss associated with magnetic disk rotation or a cable tension mounted to the rotary positioner.
That is, it is necessary to perform the servo test in the state including these magnetic head positioning error factors, which has been impossible to achieve by the existing spin stand.
(2) Second problem
The servo signal is stored alone on the magnetic disk. Therefore, as shown in FIG. 4, when the magnetic disk 1 is chucked to the spindle motor 12 of the spin stand, there is a possibility that the center position of track 21 formed by the recorded servo signal and the center position of the spindle motor 12 are deviated by a maximum of several tens to several hundreds of xcexcm, whereby readback signal from the track is observed as an eccentric signal from the rotational center of the magnetic disk (in FIG. 4, an eccentricity of a maximum size A is generated). Therefore, to follow the servo signal, it is necessary to form a control system in consideration of this eccentricity.
The above-described magnetic disk servo test can be performed, as is, in the actual HDD, however, in this case, considerable inconveniences are associated in replacement of the magnetic disk to be tested, disassembling and assembly of the positioner part and other parts replacement and the like, and problems such as damages to the magnetic disk by mistake or the like are considered. Therefore, there are problems of decreased working efficiency for testing.
In view of the above problems, an object of the present invention is to provide a magnetic media tester which can perform magnetic head positioning control in consideration of an eccentricity amount generated due to chucking under the same structure or condition as the hard disk drive of the actual machine.
In accordance with the present invention which attains the above object, there is provided a magnetic media tester comprising: a spindle motor for rotating a magnetic disk to be evaluated at a desired rotational speed, a magnetic head for testing for performing recording and reproduction to the magnetic disk, a stage provided with means for moving the magnetic head for testing at least in one direction for flexibly changing positional relation of the spindle motor and the magnetic head for testing, and a load/unload mechanism for loading the magnetic head for testing during the magnetic disk testing and unloading the magnetic head for testing after completion of the testing, wherein the stage has a thin suspension for supporting the magnetic head for testing, a thick rotary positioner for supporting the suspension, a voice coil disposed at the end side away from the magnetic head for testing of ends of the rotary positioner, a rotary shaft for supporting the magnetic head for testing, the suspension and the rotary positioner, a pair of magnets for sandwiching the voice coil, whereby positioning the magnetic head for testing on the magnetic disk by the same construction as a hard disk drive of the actual machine.
Here, in the above magnetic media tester, a lock pin contacting the rotary positioner for regulating its position is provided on the stage. By the lock pin, the magnetic head for testing is mechanically positioned on all tracks of the magnetic disk, and when the magnetic head is positioned by a readback signal from the magnetic head for testing, the lock pin is retreated to a position out of the movable range of the rotary positioner.
The above and other objects, effects, features, and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.